GEOTHERMAL GRADIENT AND HEAT FLOW IN THE BÜYÜK MENDERES GRABEN, WESTERN TURKEY

Located along the Alpine-Himalayan belt, the Büyük Menderes Graben (BMG) is an E-W oriented active extensional basin in Western Anatolia, Turkey. The BMG is one of the most important geothermal basins in western Turkey where 1500 (megawatts-energy) MW_e of installed geothermal capacity for power production exist as of December 2019.

While the BMG is a major geothermal resource, the source of the heat is not yet fully understood. Asthenospheric material that has risen beneath the eastern section of the BMG may be a regional source of heat. The geothermal gradient is reported to be variable throughout the BMG with the highest gradient in the eastern section and the lowest in the middle of the graben. However, the reason why the geothermal gradient differs so drastically throughout this region has not yet been understood.

This study aims to quantitatively test the horizontal and vertical geothermal gradients and heat flows in the Aydın-İncirliova-Osmanbükü 2015/4 Geothermal Field, which represents one field near the center of the BMG.

We have obtained well data from 12 geothermal wells in the BMG. First, we corrected bottom hole temperatures (BHT). Then we used the true vertical depth (TVD) and average surface temperature to calculate the vertical geothermal gradient. The vertical heat flow at each well is calculated using the geothermal gradient and published thermal conductivity values of the rocks penetrated at each well. Finally, heat flow modeling is used to calculate horizontal geothermal gradients and geothermal heat flow. This information is then used to create geothermal gradient and heat flow maps.

Current results show geothermal gradients of between 43.3 and 58.2 °C/km. The geothermal gradient and heat flow maps will show the changes in the vertical and horizontal geothermal gradients and heat flow, respectively, throughout the BMG. We will also determine the structural control on the geothermal gradient within the BMG.